Optimal Air Gap Research Articles

吸引・反発力を利用するハイブリッド形マイクロギャップ高トルクモータの研究

It is very effective for developing a high torque motor to keep air gap as small as possible between a rotor and a stator. By polishing the surfaces of cylindrical rotor and stators impregnated with epoxi resin, we developed a high torque motor of a hyblid type with extremely small air gaps which has no usual bearings. The rotor and stators with smooth surface play the role as a bearing.All stator poles of VR motors are not simultaneously excited, since reversal torque is generated when rotor teeth leaves stator teeth. As only attraction force is employed, halves of stator poles don't generate torque.We investigated a uniqe hyblid type motor with rare-earth bar magnets in rotor slots, in which all stator poles generate torque by employing not only atrraction force but also repulsion force. Analizing magnetic field of the hyblid motor with MAGNA/FIM, magnetic field analising software, optimum air gap geometry were aquired. We could develop a greatly higher torque motor than a VR type motor with the same size which was developed before [7].

A high-performance edge heater for the hot strip mill

A transverse magnetic flux type of induction edge heater for hot strip mills that can sufficiently heat the edge portion of a transfer bar from the very head end to the very tail end was developed. This was accomplished not only by applying the magnetic flux leakageless C-type edge heater that consists of a single magnetic circuit but also by developing an algorithm for setting the optimum air gap between the upper and lower inductors and the firing angle compensation circuit. This circuit enables the main power source thyristor inverter to be operated even when the applied load is so light that the thyristor devices of the inverter cannot commutate without the circuit. Mechanical characteristics inspections of hot strips heated by the edge heater show that the elongation characteristic of the edge parts is improved from the head to the tail end of hot strips. From this it is possible to obtain uniform distribution of the elongation characteristic all along both the width and length of hot strips. Thus, the contribution of the new edge heater to the improvement of the quality and yield rate of hot strips has been confirmed. >

An Analysis of Air Breakdown in Electrostatic Recording

Air breakdown between a very small stylus and a dielectric layer, as is often used in electrostatic recording, has been studied both theoretically and experimentally. In the experiments, styli of 60-pm diameter were placed aginst the dielectric layer of various thicknesses with an air gap of 1-60 pm. Breakdown time lag and breakdown voltage was thereby clarified as follows. 1) The logarithm of the mean statistical time lag is proportional to the logarithm of the repetition rate of breakdown and is inversely proportional to field strength in the air gap. 2) Breakdown voltage in electrostatic recording as a function of the air gap agrees well with the modified Paschen curve obtained in previous experiments using large plane parallel electrodes. These results clarify the limitation of the recording speed, the minimum recording voltage, and optimum air-gap length in electrostatic recording.

A seasonally adjusted concentrator with modifications of absorber shape

The heat losses from concentrating solar collectors can be reduced by thermally isolating the absorber with an optimal air gap between the absorber and the glass cover. However, in reflectors attempting to attain maximum optical concentration, some of the reflected rays will escape through this gap, resulting in increased losses. A concentrator was fabricated and tested with a plane tubular absorber, the results having been reported earlier. The present paper describes a design procedure for an absorber which avoids the ‘optical’ losses through the air gap. The results for the modified absorber are compared with those for the plane tubular one. The intercept factor is improved from 0·8 to 0·92. The surface area of the modified absorber is about 9 % larger than that of the plane tubular one, but the shape is such that the overall heat loss factor is much lower. As a result, the total heat loss for the modified absorber at a temperature 100° C above ambient is only 0·2 % higher than that of the plane tubular one. The improved performance curves are shown. The absorber design is also acceptable from the point of view of strengths of the components involved.

A quality factor concept for evaluation of the surface type gamma-ray backscatter soil density gauges

The major sources of error for the surface-type, gamma-ray scatter soil density gauges are identified as sensitivity to soil composition, surface roughness, and counting rate measurement errors. Methods of measuring these errors are outlined and a quality factor is proposed which properly combines these errors into a single parameter suitable for gauge evaluation. Typical values of these errors and the quality factor are reported for commercial gauges. Results are also given for the air-gap ratio method and the air-gap nomograph method. A method for determining the optimum air-gap height based on obtaining the maximum quality factor is demonstrated for a specific commercial gauge.

The Optimum Design of the Toroidal Resonator

The optimum design of a class of toroidal resonators which are capacitively loaded and therefore short in wavelengths is considered. The possibility of including magnetic cores with various types of air gaps is included and it is shown that below a certain critical size, which is a function of the magnetic merit factor, the net Q may be improved with the optimum material and the optimum air gap. Even without magnetic cores these resonators obtain a higher Q per unit volume than any other known electrical resonator.

Inductors biased with permanent magnets

IT HAS LONG been known that when a highly unsymmetrical (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf> ≠ I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> ) current magnetizes a closed iron core in an inductor or transformer, the optimum design includes an air gap in the core to reduce saturation. The presence of the air gap has two opposing effects: (1) it increases the reluctance of the core to both the biasing (d-c) magnetization and the incremental (a-c) magnetization, and (2) the shift of magnetic operating point due to (1) reduces the reluctance of the iron to the incremental magnetization. If a permanent-magnet slab is used as a counterbiasing means instead of an air gap, the magnetic operating point may be shifted toward the maximum incremental permeability point with a gap much shorter than the optimum air gap. The direct increase in reluctance is then much smaller than in the air-gap case, and the inductance is much larger. A given core size can supply a larger inductance or, conversely, a smaller permanent-magnet-gapped core can supply the same inductance as a larger air-gapped core.

The launching of surface waves by a magnetic line source

The paper deals with the idealized problem of the excitation of surface waves along two infinite, identical, separate and parallel dielectric slabs by a magnetic line source (slot). The problem is reduced to a superposition of simpler ones, namely two parallel slabs with symmetrical excitation and two parallel slabs with antisymmetrical excitation.The simplified problems are solved by the modal-analysis approach, and the synthesis of the modal components is carried out to obtain the far fields excited by the magnetic line.Radiation pattern, total power of the surface waves, total radiation loss and the efficiency of launching the surface wave are derived and computed numerically for various thicknesses of the slabs, various air-gaps between the slabs and different positions of the magnetic line source. The theoretical results indicate that, for each thickness of the slabs, high efficiency is obtained with an optimum location of the source and an optimum air-gap. Moreover, the thicker the slabs, the higher is the maximum efficiency. The thickness of the slabs and the air-gap are ultimately limited by the requirement that only one surface wave should exist for the structure.

Induction torque and servo-motor design

IN CERTAIN APPLICATIONS for an induction motor, the performance at standstill is of predominant interest. A control motor, such as a torque motor or servo motor, falls into this category. In designing such a motor, one of the usual goals is to obtain maximum stall torque. A better criterion is to maximize the ratio of stall torque to stall input power, because the allowable power dissipation of the motor is essentially invariant. This criterion is used to derive the optimum rotor resistance, the optimum number of poles, and the optimum air-gap diameter of a control motor with prescribed outline dimensions.

Optimum air gap for various magnetic materials in cores of coils subject to superposed direct current

Optimum air gap for various magnetic materials in cores of coils subject to superposed direct current

Optimum air gap for various magnetic materials in cores of coils subject to superposed direct current

A method is developed for calculating optimum air gap and core size for choke coils whose windings must carry direct current in addition to alternating current. It is employed with data on typical magnetic materials to give curves from which design dimensions can be obtained readily to fulfill specified requirements for inductance, resistance, and d-c burden.

Optimum Air Gap for Various Magnetic Materials in Cores of Coils Subject to Superposed Direct Current

A method is developed for calculating optimum air gap and core size for choke coils whose windings must carry direct current in addition to alternating current. It is employed with data on typical magnetic materials to give curves from which design dimensions can be obtained readily to fulfill specified requirements for inductance, resistance, and d-c burden.